The health of marine animals and plants kept in aquariums depends primarily on the cleanliness and oxygenation of the water. Examples of impurities which commonly degrade the aquarium environment are those in the form of suspended solids, such as fish feces and uneaten food, and those which are liquid or dissolve in the water, such as dissolved protein and ammonia from urea. All such impurities affect the desired chemical balance of the water; in particular, the rate of rise of the nitrate concentration of the water will affect the environment, and determines to a great extent the frequency with which the water must be changed. Accordingly, a great number of products for filtering and treating aquarium water have been developed.
In the simplest and most common filtering systems, the aquarium water is passed through one or a series of mechanical filters which trap particulate impurities. Such mechanical filters may for example comprise layers of sand, ground stone or coral, plastic beads, etc. For increasing the ease and convenience of changing the filter medium, filter pads made of a porous, fibrous or water permeable material are also used, either instead of or in addition to the filter layers of sand, etc. An obvious shortcoming of these systems is that they are poor at filtering out particulate matter significantly smaller than the size of the pores or distance between fibers, and they are not able to filter out dissolved matter or liquids at all.
One example of a filtering system using such simple mechanical filters is described in U.S. Pat. No. 4,606,821 (D'Imperio), in which the primary goal is to provide a filter compartment as an integral part of the aquarium so as to be as inconspicuous as possible. In order to provide at least limited chemical treatment of the aquarium water, denitrification bacteria are provided on the surface of gravel which covers the bottom of the aquarium as a layer. Simple mechanical filters are also used in the system disclosed in U.S. Pat. No. 4,684,462 (Augustyniak), which is primarily concerned with providing a device for maintaining a constant water level in the aquarium, and also provides prefiltering.
A system for rapid filtration of particulate matter from large amounts of water such as in fish hatcheries is described in U.S. Pat. No. 4,043,299 (Birkbeck). This system further illustrates the use of sand, granite, glass beads and other media which are themselves particulate in order to remove particulate impurities from water. In particular, it illustrates the need to alleviate the problem of clogging due to accumulation of solids, which is a weakness common to all purely mechanical filter systems. For its part, the Birkbeck device is provided with means for backwashing at least one of its filters by moving it vigorously, and requires an air blower.
The tendency of many solid impurities, in particular, paint, to float on water is exploited in the device described in U.S. Pat. No. 4,585,557 (Turnquist). This device, which is intended for use in industrial paint spray booths, utilizes a weir, and a baffle at the entrance to a take-off chamber, to concentrate, separate and skim paint from the surface of run-off water and thus to remove the waste paint. The device is not intended and is therefore unable to remove sub-surface or dissolved impurities.
One method for removing dissolved organic impurities such as proteins is commonly known as protein skimming, froth floatation, froth filtration or froth fractionizing. According to this method, the water to be cleansed is caused to flow in the presence of a stream of air bubbles, whereby the dissolved or fine particulate impurities may attach themselves to and be carried along with the bubbles. In some of the prior systems, the air bubbles may flow in the same direction as the water flow, and in other systems, counter flow may occur. When the bubbles reach the surface of the water, the impurities collect as a foam and may be skimmed off. The foam is typically discarded as a waste product. Furthermore, the bubbles help to aerate the water as they pass through it. This incidental aeration is particularly beneficial when the water is used to support marine life.
One known industrial filtration device which utilizes froth filtration is described in U.S. Pat. No. 3,775,311 (Mook). In this apparatus, air is mixed with effluent, which is broken up upon passage through a screen panel. In order to accomplish this, the device requires an electric motor to drive a rotating screen cage, which acts as a centrifugal blower. The device is designed for handling large amounts of waste water, in particular effluent waste water received from sewers; it is ill-suited for use in aquariums, in which maintaining a high level of water purity is of much greater importance than treating large water volumes.
A smaller scale frothing filter for use in aquariums is described in U.S. Pat. No. 4,333,829 (Walther). A primary objective of this device, referred to as "inlet means", is to allow it to adapt itself to changing water levels in the aquarium, so as to insure intake of water only from the surface. A second objective is to make the device as small as possible so that it may be placed directly in the aquarium. In order to accomplish these goals, the device comprises two telescopically arranged tubes--a float tube and a water discharge tube--which, while maintaining a good seal, must be able to move relative to one another.
Accordingly, the object of the present invention is to provide an aquarium filter requiring minimal maintenance, which removes from the aquarium water not only solid particulates but also dissolved organic impurities such as proteins. This is accomplished primarily in a prefilter using both mechanical filter elements and protein skimming, further filtration being accomplished in a subsequent secondary filter stage.
An additional object of the invention is to provide a filtration system which, to a much greater extent than existing aquarium filtration systems, forms a closed ecological system. In particular, the protein froth created in the prefilter is used to feed an arobic denitrification bacteria which in turn are used to reduce greatly the rate of build-up of nitrate in the aquarium water and consequently the frequency of necessary water changes.